1. Field of the Invention
The invention relates to a trailing arm suspension. In one of its aspects, the invention relates to a trailing arm suspension having a spring beam that mounts an axle without welding of the axle. In another of its aspects, the invention relates to a lower weight trailing arm suspension for use with trailer tandem axles. In another of its aspects, the invention relates to a trailing arm suspension with improved roll stability.
2. Description of the Related Art
Trailing arm suspensions are well known and commonly used in heavy-duty applications such as a tractor-trailer configuration. The trailing arm suspension typically comprises a pair of spaced trailing arm assemblies mounted to opposite sides of the vehicle, with each trailing arm assembly carrying an axle supporting the vehicle wheels.
The trailing arm assembly comprises a trailing arm having one portion pivotally mounted to a hanger bracket that depends from a vehicle frame rail. An air spring is disposed between another portion of the trailing arm and the vehicle frame rail to dampen the rotation of the trailing arm relative to the vehicle frame.
An important function of the trailing arm suspension is compliance in response to vehicle roll-induced forces. The vehicle roll-induced forces are typically created during the turning of the vehicle. As the vehicle is turned, the vehicle tends to rotate about its longitudinal axis in response to the G-forces encountered during the turn, causing one side of the vehicle to drop and another side of the vehicle to rise. This relative movement results in a corresponding relative rotational movement between the trailing arms on opposite sides of the vehicle. The suspension must be sufficiently compliant to permit some rolling of the vehicle in order to avoid undue torsional stress on the axles. However, the suspension must also be sufficiently stiff to resist vehicle roll beyond a predetermined roll angle for safety reasons. Generally, it is desirable to limit vehicle roll to a roll angle of about 2xc2xd degrees for most trailing arm suspensions. The roll angle is the arc traversed by trailer about its longitudinal axis measured relative to a horizontal line passing through the center of gravity of the vehicle.
In rigid beam trailing arm suspensions, the roll stiffness of the suspension is achieved through the mechanical torquing of the axle as the rigid trailing arms move relative to each other to twist or torque the axle. If the mechanical torquing of the axle is too great, it can cause premature failure of the axle. The suspensions are made compliant to the roll with the use of a resilient connection between either or both the pivotal connection of the trailing arms to the hanger bracket and the connection of the axle to the trailing arm. The resilient connections are typically achieved by elastomeric bushings.
An ideal trailing arm suspension is substantially compliant up through about 2xc2xd degrees of roll angle and then quickly becomes stiff to prevent the vehicle from rolling through too great of a roll angle. In other words, on a plot of roll moment versus roll angle, an ideal suspension will have a generally linear relationship between the roll moment and roll force until the compliance is exceeded then the curve will tend toward being infinite.
An alternative to the rigid beam trailing arm is a flexible beam also known as a spring beam. A spring beam typically is manufactured from spring steel that is capable of flexing in the vertical direction in response to vertical forces. One end of the spring beam is mounted to a hanger bracket by either a pinned connection or a resilient connection in the nature of an elastomeric bushing. The other end of the spring beam is rigidly mounted to the axle, usually through a bolted connection with an axle bracket that is welded to the axle, thus eliminating the need for a resilient connection between the axle and the beam. The spring beam advantageously functions much like a spring in that the response is relatively linear.
The welding of the axle to an axle bracket weakens the axle at the weld joint and ultimately results in failure of the axle. Typically, the axles must be made of sufficient thickness so that the torsional resistance of the axle at the welded joint is sufficient to meet torsional requirements for the suspension. On the other hand, non-welded axle connections can have thinner wall thickness and thus less weight and cost for the same suspension rating. Trailing arm suspensions with non-welded axle connections are disclosed in WO 97/06022, published 20 Feb. 1997.
The invention relates to an improved suspension including a pair of trailing arm assemblies adapted to mount on a vehicle frame having a pair of spaced frame rails. Each trailing arm assembly comprises a frame bracket adapted to be mounted to one of the frame rails, and a spring beam pivotally mounted at one end to the frame bracket for pivotal movement about a pivot axis and adapted to carry an axle in spaced relationship to the beam one end, for example, at another end of the beam. The suspension further includes a spring mounted to the trailing arm also in spaced relationship to the beam one end and adapted to mount to a corresponding frame rail to resist the rotational movement of the trailing arm toward the frame. According to the invention, an axle seat is integrally formed in the spring beam.
The axle seat preferably has a cylindrical-shape. The cylindrical-shape axle seat defines an axle opening that is sized for slidably receiving an axle. A portion of the spring beam can be bent, preferably about 360xc2x0, to form the cylindrical-shape that defines the axle opening.
The spring beam has a flange that extends laterally from the axle seat along a central portion of the spring beam for clamping the axle seat around the axle. The central portion of the spring beam and the flange in one embodiment have openings in registry with each other. A bolt extends through openings in the spring beam and the flange for clamping the cylindrical-shaped axle seat around the axle.
In an alternate embodiment, a fastener, such as a strap or a U-bolt, overlies a central portion of the spring beam and is clamped onto the flange. In this embodiment, the flange is formed from a separate block that is fixed, for example, by welding, to an end portion of the cylindrical-shape axle seat and is fixed to the fastener, by, for example, passing the U-bolt legs through openings in the block or welding the strap legs to the block.
In one embodiment of the invention, an axle is mounted in the axle seat in each of the trailing arm assemblies and a thin adhesive layer is disposed between the axle and the axle seat for bonding the axle to the axle seat. The axle seat is sized to substantially encircle the axle and is sprung in tension to compress the axle and evenly distribute a compressive load on the axle across at least two sets of diametrically opposed external surfaces of the axle. When an adhesive layer is provided between the axle and the axle seat, the compressive load of the axle seat on the axle in combination with the adhesive bond between the axle and the axle seat are sufficient to prevent relative movement of the axle with respect to the axle seat under ordinary service conditions.
In one embodiment, the axle seat is formed by bending another portion of the spring beam to define an axle opening that has a diameter less than a diameter of the axle when the axle seat is in an unsprung state. The other portion of the spring beam is thus in tension about the axle when the axle is mounted in the axle seat to thereby apply a compressive force to the axle.
In a preferred embodiment of the invention, the spring beam forms a traverse bolt opening for mounting the one end of the spring beam to the frame bracket for pivotal movement about a pivot axis. The spring beam has a longitudinal centerline perpendicular to the pivot axis and a longitudinal centerline transverse to the axle seat. The axle seat longitudinal centerline is located outboard of the pivot axis longitudinal centerline for greater roll stability of the vehicle. The traverse bolt opening is preferably cylindrically shaped.
In another preferred embodiment of the invention, a brake actuator is rigidly mounted to the spring beam closely adjacent the axle seat. Further, an S-cam bearing is rigidly mounted to the spring beam closely adjacent the axle seat.
Further according to the invention, a trailing arm suspension comprising a pair of trailing arm assemblies adapted to mount to a pair of spaced vehicle frame rails includes, in each trailing arm assembly, a frame bracket, a spring beam and a spring. The spring beam is pivotally mounted at one end to the frame bracket for pivotal movement about a pivot axis and has an axle seat in spaced relationship to the one end of the beam. The axle seat is adapted to carry an axle. The spring beam has a longitudinal center line perpendicular to the pivot axis and a longitudinal center line transverse to the axle seat. The spring is mounted to the spring beam in spaced relationship to the beam one end and is adapted to be mounted to one of the frame rails to resist the rotational movement of the trailing arm toward the frame. According to the invention, the axle seat longitudinal centerline is located outboard of the pivot axis longitudinal center line to increase the roll stability of the suspension.